A new Wayland::Buffer class is provided which wraps a:
* wl_buffer
* size
* stride
* memory address of data represented by the buffer
In addition the Buffer knows whether the compositor has released it or
not. This allows the ShmPool to reuse the buffer in case the same size
and stride is requested.
This is currently most relevant for the CursorData. Instead of keeping
the wl_buffer, the QImage for the cursor is kept and each time the cursor
is set for the surface a new buffer is requested from the ShmPool.
The ShmPool now either reuses an existing buffer or creates a new one.
Furthermore the ShmPool takes care of releasing all buffers at EOL.
The backend gets created by Workspace, but only if the environment
variable WAYLAND_DISPLAY is set.
Because of that the egl wayland backend does no longer create the
backend, but uses the already created one.
The functionality to create the connection to a Wayland compositor and
creating a fullscreen surface is moved into wayland_backend.(h|cpp). The
wl_egl_window for the surface is moved into the EglWaylandBackend to have
the actual WaylandBackend free from Egl. This will allow in future to
implement other compositing backends for Wayland which do not use egl.
This means that egl is no longer a build requirement for the wayland
related functionality.
